Called the Codex Leicester, Gates scooped up the notebook for $30.8 million in 1994, making it the most valuable manuscript in the world. If you want to play with it, check out the British Library's digitized version. But why does Gates, who's at work reinventing the nuclear reactor, keep coming back to a 500-year-old journal?

"It's an inspiration that one person—off on their own, with no feedback, without being told what was right or wrong—that he kept pushing himself," Gates says, "that he found knowledge itself to be the most beautiful thing."

The notebooks show an incredible mind at work: In the video, you can see da Vinci's approximations of the movement of water, looking for the roots of turbulence. The sketches showcase the inventor's brilliance—and more endearingly, how Gates, as his friend Warren Buffett would like to see, admires his hero.

Da Vinci and Gates, of course, are not that uncommon: As 60 Minutes reporter Charlie Rose observes, the Microsoft founder is "similarly obsessed with understanding the world," as evinced by his rows of books on meteorology, geology, philosophy, and fertilizer.

Why would a billionaire want to know so much? Gates, like other innovators, sees the intersectionality of learning: "The more you learn," he says, "the more you have a framework that the knowledge fits into."

Bottom Line: Connect with your heroes. And maybe buy their notebooks if you've got the scratch.